Madison Gas and Electric Company Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	MGE [Member]	Cumulative Effect Period Of Adoption Adjustment [Member] MGE [Member]	Cumulative Effect Period Of Adoption Adjusted Balance [Member] MGE [Member]	Common Stock [Member]	Common Stock [Member] MGE [Member]	Additional Paid-In Capital [Member] MGE [Member]	Retained Earnings [Member] MGE [Member]	Retained Earnings [Member] Cumulative Effect Period Of Adoption Adjustment [Member] MGE [Member]	Retained Earnings [Member] Cumulative Effect Period Of Adoption Adjusted Balance [Member] MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member] MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member] Cumulative Effect Period Of Adoption Adjustment [Member] MGE [Member]	Accumulated Other Comprehensive (Loss)/ Income [Member] Cumulative Effect Period Of Adoption Adjusted Balance [Member] MGE [Member]	Noncontrolling Interest [Member] MGE [Member]
Beginning balance, shares at Dec. 31, 2017					34,668	17,348
Beginning balance, value at Dec. 31, 2017		$ 632,774	$ 0	$ 632,774		$ 17,348	$ 192,417	$ 282,135	$ (28)	$ 282,107	$ (28)	$ 28	$ 0	$ 140,902
Increase (Decrease) in Equity [Roll Forward]
Net Income	$ 84,219	79,036						56,484						22,552
Capital contributions from parent		0
Distributions to parent from noncontrolling interest		(22,000)												(22,000)
Ending balance, shares at Dec. 31, 2018					34,668	17,348
Ending balance, value at Dec. 31, 2018		689,810				$ 17,348	192,417	338,591			0			141,454
Increase (Decrease) in Equity [Roll Forward]
Net Income	86,874	80,779						58,430						22,349
Capital contributions from parent		30,500					30,500
Distributions to parent from noncontrolling interest		(23,500)												(23,500)
Ending balance, shares at Dec. 31, 2019					34,668	17,348
Ending balance, value at Dec. 31, 2019		777,589				$ 17,348	222,917	397,021			0			140,303
Increase (Decrease) in Equity [Roll Forward]
Net Income	$ 92,418	85,523						63,130						22,393
Capital contributions from parent		30,000					30,000
Distributions to parent from noncontrolling interest		(21,500)												(21,500)
Ending balance, shares at Dec. 31, 2020					36,163	17,348
Ending balance, value at Dec. 31, 2020		$ 871,612				$ 17,348	$ 252,917	$ 460,151			$ 0			$ 141,196